Exactly. Every GPSRb works by adjusting the C-field: sort of let me (the algorithm/GPS pair) calibrate your Rb for the long term (aging) variation that every Rb has. The Rb is not good in the long term (100000 seconds), not as good as a working and receiving GPS receiver. The Rb (as a whole) *is* an expensive OCXO that has good short term stability, paired with a disciplining algorithm and a GPS it becomes like a Cs (and maybe even better in the short term).
On Wed, Aug 22, 2012 at 6:03 PM, Bob Camp <li...@rtty.us> wrote: > Hi > > The problem you run into with this approach is that it is relatively high > jitter. You output "jumps" by what ever your microcontroller step time step > size is every so often. Since that's going to be 10's or possibly 100's of > ns, it's a major hit. > > Bob > > -----Original Message----- > From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On > Behalf Of Michael Tharp > Sent: Wednesday, August 22, 2012 10:47 AM > To: time-nuts@febo.com > Subject: Re: [time-nuts] GPSD-Rb > > On 08/22/2012 01:22 AM, Edgardo Molina wrote: > > b. Is it possible to build a GPSDRb? I would like to know if it is > reasonable to pursue the goal to discipline the 5065a with a TB which I > also > got recently. > > Some Rbs have a "C-field" input that can technically be used to > discipline it, but this is not the approach I am going to take with > mine. A Rb oscillator is internally an OCXO that is disciplined to the > Rb physics package, with the goal of holding a frequency over a long > period of time with the only variance coming from deficiencies in the > measurement circuitry. Using the C-field to discipline it is kind of > throwing out the long-term stability characteristics of the Rb and using > it as an expensive OCXO. It's more interesting to me as a holdover > source for a conventional GPSDO. > > The design I'm thinking of is to have a separate microcontroller clocked > by the Rb that will generate a third pulse-per-second (the first two > being the raw one from GPS and the divided-down local oscillator). As > long as the GPS is locked the divider will not output pulses but will > monitor the pulses from the local oscillator and use it to count the > frequency of the Rb. Once lock is lost or holdover is manually engaged, > then it stops counting and starts outputting pulse-per-second based on > the last known average frequency it counted. The GPSDO would then > continue normal disciplining based on the Rb pulses until GPS lock > returns. Of course while locked the measured frequency would also be > reported so that the Rb could be calibrated in situ. > > -- m. tharp > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.